Studies will be done to determine the mechanisms by which BCG produces resistance to certain tumors, and by which iodoacetamide-killed Friend disease cells produce resistance to Friend virus infection. Employing Hibbs' technique, the activity of macrophages from normal and BCG-immune mice will be evaluated in terms of their ability to inhibit growth of melanoma cells (B16) in vitro. The ability of BCG-immunized mice to mount a specific immune response to B16 cells will be studied, employing macrophage inhibition tests and leucocyte adherence tests, as suggested by Holliday, et al., colony inhibition tests as described by Takasugi et al., and fluorescent antibody studies. It is of importance to determine if nonspecifically immunized animals eventually develop specific resistance to a given tumor. In order to determine specificity, another tumor which arose in C57Bl/6 mice will also be employed. Further studies of oil cell wall vaccines for prevention of tumors will be made. Although this vaccine is extremely effective in preventing pulmonary tuberculosis in mice our results do not show it to be equal to BCG for prevention of tumor growth when tumor cells are given intravenously.